Problem with throttle

Davie Sprocket · Post by **Davie Sprocket** » Sat Jun 28, 2008 11:56 am

My 420 runs good but, when i pull down on the throttle the motor revs up a bit but then stumbles and the rpm drops down or it stutters. I've played with the carb and timing as well as the points and have no success rectifying this issue. Could it be something with the governor assembly. The carb is a repo zenith i think. Its very frustrating, not being able to get above idol. Using my manual i have checked most of the settings but haven't gotten into taking anything apart. Any help would be really cool.

Dave

Paul Buhler · Post by **Paul Buhler** » Sat Jun 28, 2008 7:03 pm

I'd suggest carefully taking the carburetor apart. You might have a partially plugged screen or a bit of something in one of the jets or pathways. A rebuild kit is cheap and the job is easy to do with some patience, compressed air and carb cleaner. If the carb has bigger issues, at least you'll know, and have eliminated one of the easier fixes, and if it works, you're ahead of the game. Good luck. Paul

Eric.MacLeod · Post by **Eric.MacLeod** » Sat Jun 28, 2008 8:39 pm

i think your carb is the problem also, take your air cleaner off and have someone rev it up when it starts to stutter spray some gas in it from a small squirt bottle , if it revs up or smooths out it was to lean, if it chokes up than fuel is not your problem, also is the tank screen plugged up?

CELSESSER · Post by **CELSESSER** » Sun Jun 29, 2008 7:34 am

Davie,
The 420 originally came with a Marvel/Schebler TSX series carb on them. The name is pretty obvious on the side of the bowl. If it does have a Marvel/Schebler on it I can help you out with the service manual if you send me a PM with your e-mail address. Carbs and fuel systems on old and especially unused equipment is the first thing I look at after determining that I have spark. I just got a International 666 going that had been dead for 6 years. After pulling a couple plugs and squirting a little gas in and replacing the plugs it fired a few times, then I removed the card and cleaned it though it had no obvious obstructions and replaced it. Then I removed the filter bowl from the bottom of the fuel tank and blew a big wad of crap backwards out of sediment bowl housing. Put it back together with some FRESH gas and fired right up and purred like a BIG kitten.

Chuck

Paul Buhler · Post by **Paul Buhler** » Sun Jun 29, 2008 11:25 am

Dave:
If you send me your email address, I can send you a PDF manual with the Marvel and Zenith schematics and other information on them.
Paul

Davie Sprocket · Post by **Davie Sprocket** » Mon Jul 21, 2008 12:15 am

Okay finally got a shot at the carb today, i took it all apart cleaned it, resurfaced the lower half to clean off the gasket. I put it all together, got it back on the crawler. Fired right up and held idle, i set the idle screw, let it warm up then i started pulling the throttle and it still revs and then stutters. I played with the power valve and i seem to have that set decently, but it is still doing what it was before. Is the power valve possibly to blame. After shutting it down fuel started to come out of the carb, so i pulled it apart to see if the float valve was stuck but it looked fine, put it back together and ran it some more, then shut it off again, same thing fuel started to spill out. I'm gonna have to drain the tank and see if that has some restriction. I regauged the points, just in case i missed that, otherwise i'm basically spitting in the wind.

Dave

Post by **Lavoy** » Mon Jul 21, 2008 8:21 am

You have a fuel starvation issue I would bet, double check to make sure that you have adequate fuel flow from the sediment bowl. I have had exactly the same problem myself on several machines, it turned out that something had plugged the inlet to the sediment bowl, and restricted the fuel flow.
Lavoy

Tigerhaze · Post by **Tigerhaze** » Mon Jul 21, 2008 9:24 am

I have a Marvel/Schebler TSX series carb on my 8N tractor- I have found that another issue (especially if it has sat for a while) is for the float and/or fuel inlet needle to get gummed up and stick and cause fuel starvation. I have alos had the float stick the opposite way (down) and have fuel overflow.

It sounds like you went through the carb so you wouldn't expect that problem, but maybe the float arm is binding?

H-D · Post by **H-D** » Mon Jul 21, 2008 5:45 pm

If you should find "no joy" in the fuel system, check the centrifigal advance unit in the distributor by watching for advance with timing light while creeping the throttle up.

lizrad999 · Post by **lizrad999** » Mon Jul 21, 2008 10:29 pm

HD you took the words right out of my mouth!
My 440IC's advance unit was rusted in place. Had to pull the Dist. and disassemble the thing to get it back working.
You can find this mechanism under the plate that holds the points. To get her completely apart, there is a taper pin down at the end that goes into the oil pump. Drive that pin out and the shaft should slide out (if I remember correctly......)
Worth checking anyway.

Davie Sprocket · Post by **Davie Sprocket** » Mon Jul 21, 2008 11:28 pm

I'll pull the dist and do what you say. I haven't gone that far with the distributer. Bad news is i broke the bowl inlet when i was trying to get it off the tank, i found some rust in the tank as well. I'm gonna have to get another fuel bowl and then go from there, i got it off and it looked bad but the screen was taken out of it along time ago, plus i took the screen out of the carb and it looked pretty good. I think while i'm ordering the fuel bowl i'll get the parts to rebuild the dist and some other stuff. I put an inline fuel filter between the fuel bowl and carb but haven't got to try it as i broke the fuel bowl after that. I'll keep posting until i get this solved. Any more ideas are appreciated.

Dave

Davie Sprocket · Post by **Davie Sprocket** » Wed Aug 06, 2008 9:58 pm

Okay i finally got a chance to tear into the distributer and ended up using the one from my 40, now i replaced the fuel bowl. I was trying to start her but all she's doing right now is back fire, moving the dist around trying to get it to fire and no luck. Any ideas what i'm doing wrong.

Dave

H-D · Post by **H-D** » Wed Aug 06, 2008 11:07 pm

She's gotta be 180 degrees out on the spark timing to backfire. Maybe the 40's distributor times 180 out from the 440? Try swapping the spark plug wires just for grins & see if the ol' girl won't light up.

H-D · Post by **H-D** » Wed Aug 06, 2008 11:07 pm

She's gotta be 180 degrees out on the spark timing to backfire. Maybe the 40's distributor times 180 out from the 440? Try swapping the spark plug wires just for grins & see if the ol' girl won't light up.

Davie Sprocket · Post by **Davie Sprocket** » Thu Aug 07, 2008 10:06 am

Yeah i was basically thinking that, i'll rotate the entire dist around, the distributor rotor only fits into the drive one way, so i think i need to rotate the body and see if i can get er to fire.

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